An epoxy resin composition for a fiber-reinforced composite material containing a phosphorus-containing epoxy resin, dicyandiamide as a curing agent, and a curing accelerator having a specific structure has been proposed in the past (for example, see Japanese Unexamined Patent Application Publication No. 2012-233133A). By setting the compounded amount of the phosphorus-containing epoxy resin to within a prescribed range in this epoxy resin composition for a fiber-reinforced composite material, it is possible to prevent decreases in the strength of the cured product and to achieve sufficient flame retardancy without using halogen-containing compounds, antimony trioxide, and the like. In addition, using a curing accelerator having a specific structure in combination with dicyandiamide as a curing agent makes it possible to realize curability at low temperatures and excellent storage stability.
Incidentally, in the field of structural materials and interior materials for aircraft, fiber-reinforced composite materials are widely used as a face plate for a honeycomb panel from the perspective of weight reduction. In recent years, self-adhesive technology for directly adhering a honeycomb core and a prepreg obtained using an epoxy resin composition for a fiber-reinforced composite material has come into the spot light in order to further reduce the weight and production cost of honeycomb panels.
However, in the case of the epoxy resin composition for a fiber-reinforced composite material described in Japanese Unexamined Patent Application Publication No. 2012-233133A, although it is possible to reduce the environmental impact because halogen-containing compounds and antimony trioxide are not used, it is not necessarily possible to achieve sufficient adhesiveness with respect to the honeycomb core. Therefore, there is a demand for an epoxy resin composition for a fiber-reinforced composite material which yields excellent flame retardancy without using halogen-containing compounds and antimony trioxide, has excellent curability at low temperatures and storage stability, and yields high adhesiveness with respect to a honeycomb panel.